The present invention relates to digital electronic wristwatches and more particularly to an alarm mechanism for such watches which produces an audible sound to warn the wearer of the occurrence of a predetermined time.
Microelectronic circuitry has made possible the manufacture in increasing numbers of digital readout electronic wristwatches, many of which operate as completely solid state devices without moving parts or other mechanisms which limit the usable life of mechanical timepieces. Such watches are normally supplied with electrical power by one or two miniature batteries which are sufficient to drive the oscillators and counters used for controlling and storing a time count and for at least intermittently displaying the time. Prior art attempts, however, to integrate within the small confines of a wristwatch an audible alarm system have been relatively unsatisfactory. The primary difficulties which have prevented satisfactory alarm watches from being produced are the extremely tight physical space limitations combined with the power limitations imposed by the miniature batteries which must be utilized in these devices. As a consequence, prior art alarm wristwatches, while in some instances producing a barely audible alarm, have not in general produced a strong audio signal while at the same time conserving battery capacity.
An additional constraint which has not been satisfactorily overcome in the prior art is imposed by the fact that the optimum location for a vibrating alarm member within a watch structure is along the rear cover of the watch, that is, between the battery compartments and the rear cover. This presents difficulties in regard to the electrical connections which must be made to the vibrating alarm mechanism, since the watch back as well as the vibrating member must typically be removed in order to change the watch piece batteries. A satisfactory method for mounting the vibrating element and for electrically connecting this element to the electronic system of the watch has not heretofore been developed.
Prior art alarm watches using piezoelectric crystals as audio transducers have typically mounted such crystals against flat, rigidly mounted watch surfaces. The crystals in such watches must overcome not only the mechanical stiffness of the watch surface itself to vibrate this element and thereby provide an audible alarm, but must also overcome the increased vibration resistance caused by the rigid mounting of the watch surface. Thus, the sound output of such alarm is typically insufficient unless oscillating circuits, including space consuming inductors, are utilized.